1. Field of the Invention
The present invention relates to floor panels composing the free access floors of OA (Office Automation) rooms, general business offices, etc. which accommodate various types of equipment, such as office automation devices, computers, etc.
2. Prior Art
Free access floor panels used conventionally include those made of aluminum alloys, steel, inorganic materials of concrete system, etc., synthetic resins, and wood.
The free access floor panels are shaped into quadrates, and laid directly on the floor or installed such that they are supported on a specified level by props. The floor thus formed is called a "free access floor", and in many cases, the very heavy equipment, such as computers with peripheral devices, and other OA devices, are installed thereon.
The floor panels for the free access floor made of metals, such as steel, and aluminum alloys include bottom plates having a reinforced construction with uneven surfaces integrated with nearly square top plates. Carpeting made of woven fabrics and unwoven fabrics, or sheets of synthetic resin tiles, etc. are bonded on the upper surfaces of the top plates as finishing materials.
The characteristic features of conventional free access floor panels in terms of the material quality are described as follows:
Conventional floor panels made of aluminum are of merit because they have a high degree of finishing precision, but they also have the following drawbacks. For instance, since the aluminum used for this type of floor panel has a Young's modulus which is about one third that of steel, it is necessary for the aluminum panel to be used in a weight adequate enough to have a Young's modulus similar to that of a steel panel so as to obtain the required strength. This, however, naturally invites increases in cost. Furthermore, since such panels require die casting machine work for its manufacture, productivity is lower in comparison with steel floor panels.
Panels using inorganic materials such as a concrete system, etc. are superior in fire resistance and also low in cost. However, they are generally weak to impact and therefore, are not suitable to be used in a form of a large panel. Besides, since they are heavy, it is difficult to execute construction and layout when using them. Also, it is not desirable to use them in buildings. In addition, they have the disadvantage of creating the dust and easily chipping. Consequently, they are usually covered with steel pans and carpeting materials (for example, U.S. Pat. No. 3,811,237).
Panels made of synthetic resin and wood are advantageous in that they are low in cost and light in weight. However, they are inferior in fire resistance since they easily burn. Also, since they are low in strength, they are laid directly on the floor or used as small panels and thus their use is limited. Therefore, countermeasures must be taken such as covering them with steel sheets so as to improve fire resistance and strength (U.S. Pat. No. 4,035,967 and USP 4,085,557).
The conventional panels made of steel have advantages in that they are as light weight as aluminum and about one half the weight of concrete system material. They are also high in strength, and have less deflection because the Young's modulus of steel is about three times that of aluminum. However, when the panels are manufactured by be welding as is conventionally done to secure high strength even though they are hollow (for example, U.S. Pat. Nos. 3,380,217 and 3,696,578), the welded portions are burnt and oxidized even if the surface treated steel sheets are used for rust prevention, resulting in the formation of rust. Consequently, these panels have the disadvantage in that they need the rust prevention treatments, such as coating after the assembly.
The structural features of conventional free access floor panels will be described below.
Because the floor is formed by laying out identical plates for the entire floor, when there is a difference in the direction and height at the four corners of the free access floor panels, weakness and instability is caused. Therefore, it is necessary to manufacture flat panels with a great degree of accuracy. Also, during installation if the degree of flatness of the underfloor ground is not satisfactory, it will result in floor surface being unsteady. As a result, installation requires a lot of time and labor in order to adjust the unsteadiness. A countermeasure taken against shakiness is to make the panel material into a triangular shape so that shakiness is prevented by forming an aggregate of three-point supporting components. With this countermeasure, even though the panels are virtually square in shape, they are bendable along their diagonal lines, thus solving the foregoing problem (e.g. U.S. Pat. No. 3,852,928).
The inside of a room in which the free access floor is installed needs, for the purpose of maintenance of the equipment therein, a specified temperature be maintained and minimization of noise cased by walking as well as sounds coming from the equipment. The disadvantages of conventional free access floor panels in view of these requirements are as follows.
To achieve sound insulation and thermal insulation to a certain extent, synthetic resin tiles and carpeting materials are bonded to the upper surfaces of the top plates, but such measures are neither sufficient nor positive as a means to solve these problems sufficiently. It has also been attempted to fill the inside of the floor panel with foam concrete as part of the countermeasures, but it is not easy to inject the concrete into the panels. Thus, there has been a problem with its workability. Furthermore, as another attempt, CFRC (carbon fiber-reinforced cement) and GRC (cement reinforced with glass fiber) have been packed inside of the floor panels, but this also has its drawbacks including a high degree of shrinkage/distortion, heavy weight and high cost.